This application claims the priority of German Application No. 10 2005 055 996.4, filed Nov. 24, 2005, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a drive device for a motor vehicle having a multi-cylinder internal combustion engine, where each cylinder includes at least two outlet valves, where at least of one of the at least two outlet valves can be controlled in regard to its stroke, and at least two exhaust gas turbocharger devices are provided.
The most varied drive devices with an internal combustion engine and at least two exhaust gas turbocharger devices are already known. In the trade journal MTZ, 5/2005, Annual Edition 66, an internal combustion engine with two exhaust gas turbocharger devices connected in series has already been described under the title “Der neue BMW-Sechszylinder-Dieselmotor mit Stufenaufladung” [The New BMW Six-cylinder Diesel Motor with Variable Charging].
It is an object of the invention to provide a drive device having an internal combustion engine and at least two exhaust gas turbocharger devices that is improved in regard to the response behavior of the turbocharger devices. Furthermore, the drive device is intended to be improved with regard to the maximum power that can be produced by it.
According to the invention, the objective is achieved by providing a drive device including a multi-cylinder internal combustion engine, where each cylinder includes at least two outlet valves, where at least of one of the at least two outlet valves can be controlled in regard to its stroke, and at least two exhaust gas turbocharger devices are provided. At least one outlet valve of each cylinder is assigned to at least one exhaust gas turbocharger device in such a manner that the exhaust gas duct assigned to this outlet valve is connected to the turbine wheel of the exhaust gas turbocharger device. Further preferred embodiments of the invention are described and claimed herein.
According to the invention, it is provided to form each cylinder of the internal combustion engine with at least two outlet valves, where at least of one of the at least two outlet valves is formed as a valve (or valve drive) with variable stroke or with variable stroke and variable control time (variable valve timing). Furthermore, it is provided to assign to one of the at least two exhaust gas turbocharger devices of each cylinder at least one first outlet valve, and to assign to the other exhaust gas turbocharger device of each cylinder at least one other, second outlet valve. In so doing, the assignment is done by the assigned outlet valve being connected, via a separate outlet or exhaust gas duct, to the turbine wheel of the assigned exhaust gas turbocharger device. A plurality of outlet or exhaust gas ducts is provided per cylinder.
Preferably, a total of two exhaust gas turbocharger devices are present and each cylinder includes precisely two outlet valves (a variably controllable outlet valve and an outlet valve with at least fixed stroke curves or with fixed stroke and control time curves), where the non-controllable outlet valve of each cylinder is assigned to the first exhaust gas turbocharger device and the controllable outlet valve of each cylinder is assigned to the second exhaust gas turbocharger device. Advantageously, the one outlet valve or all the outlet valves of all the cylinders are variable with regard to their control time curves via a controllable displacement of the cam shaft (the outlet valves designated in the sense of the invention as controllable outlet valves as well as the outlet valves designated in the sense of the invention as non-controllable outlet valves). In the sense of the invention, a controllable outlet valve is understood to mean an outlet valve that is formed in such a manner that it can be controlled at least with regard to its stroke curve. The switching off of the controllable outlet valve is accomplished by the stroke of this outlet valve being set equal to zero.
In a preferred embodiment of the invention, the first exhaust gas turbocharger device is embodied as a so-called twin-scroll charger and the second exhaust gas turbocharger device is embodied as a so-called dynamic pressure charger. In motors with six or more cylinders, it can be reasonable to embody the second exhaust gas turbocharger device also as a twin-scroll charger in order to achieve, even for higher intake volume flows, a group separation of the cylinders on the exhaust gas side and thus to avoid the negative interaction of the cylinders thrusting out one after the other in the ignition sequence. With this, the residual gas content in the combustion space can be reduced and the requirement for charge pressure can be reduced. The exhaust gas turbocharger devices are preferably dimensioned differently, in particular the first charging device is formed for a low rotary speed range or a low volume flow via the compressor, and the second charging device is formed for a rotary speed range extending the first rotary speed range upwards or a greater volume flow via the compressor. In doing so, the rotary speed of the motor is only indirectly a measure for the difference of the two ranges. What is important here is the volume flow conducted via the compressor of the exhaust gas turbocharger unit, or the corresponding operating point in the characteristic diagram for the compressor (volume flow via the compressor over pressure ratio over the compressor). In the following we will refer to the volume flow over the compressor to distinguish the two ranges. Included in the sense of the invention are, however, all the parameters, such as, for example, the rotary speed of the motor, which correlate at least in operational subranges to the volume flow.
To increase the maximum power which can be generated by the internal combustion engine, the first exhaust gas turbocharger device is connected on the exhaust side of the turbine wheel to a series circuit of an initial catalytic converter and the principal catalytic converter, while the second exhaust gas turbocharger device is only conducted by the output side of its turbine wheel to the main catalytic converter.
Furthermore, a control device is provided which, in a lower volume flow range up to a predetermined volume flow threshold value, drives the controllable outlet valves in such a manner that they are in a closed position. In this lower volume flow range, the exhaust gas to be ejected from the cylinder combustion chambers is accordingly fed only via the outlet and exhaust gas ducts of the non-controlled outlet valves of a single exhaust gas turbocharger device (or the first exhaust gas turbocharger device). Thereby, it is achieved that, in the lower volume flow range only, one exhaust gas turbocharger device (in particular an exhaust gas turbocharger device of low mass, since this is designed exclusively for the lower rotary speed range) has to be accelerated and the compressor of this charging device moves in a characteristic diagram with better efficiency. A valve that can be driven by the control unit closes, in the lower volume flow range, the compressor outlet of the other compressor (compressor of the second exhaust gas turbocharger device) in order to prevent the outflow of the compressed intake air via the inactive compressor.
On overshoot of the predetermined volume flow threshold value, in an upper volume flow range, the controllable outlet valves are in addition driven in such a manner that also via their outlet and exhaust gas duct a part of the exhaust gas flow to be ejected can be conducted away. This partial exhaust gas flow is conducted to the second exhaust gas turbocharger device. Thereby it is achieved that, in an upper volume flow range, intake air can be additionally compressed and supplied to the cylinder combustion chambers. The maximum power is further increased since the exhaust gas counter pressure is reduced due to the initial catalytic converter not being present and thus the possible drops in pressure over the turbines of the exhaust gas turbocharger device and the efficiency of the combustion is improved by the reduction of the amount of residual gas.
Furthermore, a reduction of emissions is achieved through the invention since the catalytic converter temperature required for conversion is reached earlier after a cold start due to the reduction of masses to be heated up. During the catalytic converter heating phase the controllable outlet valve of the cylinders is closed in each case so that the volume flow is conducted via only one exhaust gas turbocharger device. The mass of this exhaust gas turbocharger device is less than that of a single large exhaust gas turbocharger, which would also have to be implemented by itself for the entire exhaust gas mass even at the nominal power point.
In the catalytic converter heating phase, the first exhaust gas turbocharger, which is preferably dimensioned to be smaller, is active and the second exhaust gas turbocharger, which is preferably dimensioned to be larger, is inactive. Due to the high exhaust gas enthalpy required for heating the catalytic converter device, the compressor of the first exhaust gas turbocharger can convey more intake air than the combustion motor needs. The excess intake air can be conducted away via the compressor of the second exhaust gas turbocharger device. The compressor of the second exhaust gas turbocharger device is thereby set in rotation. By the rotation it is prevented that the otherwise stationary, inactive exhaust gas turbocharger ceases to be oil-tight at the connecting shaft between the turbine and compressor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.